Method for reducing fouling in a refinery

ABSTRACT

A method and apparatus for reducing fouling associated with a process stream in a heat transfer component. The method and apparatus include the use of one of a vibration producing device to impart a vibrational force to desired component and a pulsation producing device for apply pressure pulsations to the process stream. The heat transfer component has at least one surface having a surface roughness of less than 40 micro inches (1.1 μm).

CROSS REFERENCE TO RELATED APPLICATION

This application relates to and claims priority to U.S. ProvisionalPatent Application No. 60/751,985, filed Dec. 21, 2005, entitled“Corrosion Resistant Material For Reduced Fouling, A Heat ExchangerHaving Reduced Fouling And A Method For Reducing Heat Exchanger Foulingin a Refinery” and U.S. Provisional Patent Application No. 60/815,844,filed Jun. 23, 2006 entitled “A Method of Reducing Heat ExchangerFouling in a Refinery,” the disclosures of which are hereby incorporatedherein specifically by reference.

FIELD OF THE INVENTION

This invention relates to the reduction of sulfidation or sulfidiccorrosion and the reduction of depositional fouling in general and inparticular the reduction of sulfidation or sulfidic corrosion and thereduction of depositional fouling in heat transfer components, whichinclude but are not limited to heat exchangers, furnaces and furnacetubes located in refining facilities and petrochemical processingfacilities. In particular, the present invention relates to thereduction of corrosion and fouling associated with heat transfercomponents used in the context of a crude oil refinery and petrochemicalprocessing applications. The present invention relates to improvedheat-transfer components which exhibit improved corrosion resistance andimproved resistance to fouling by combining the use of a corrosionresistant material with the application of vibration, pulsation or otherinternal turbulence promoters. The present invention is directed to amethod of reducing fouling in a heat exchanger, which combines the useof a corrosion resistant material with the application of vibration,pulsation or internal turbulence promoters. The present invention isalso directed to a method of reducing fouling in existing and new heattransfer components for use in refining and petrochemical processingapplications. The present invention is also directed to a method ofreducing sulfidation or sulfidic corrosion and fouling.

BACKGROUND OF THE INVENTION

Heat transfer components are used in refinery and petrochemicalprocessing applications at various locations within the facilities toadjust the temperature (i.e., heat or cool) of the processed fluid(e.g., crude oil or derivatives thereof). The heat transfer components(e.g., a heat exchanger, furnaces, and furnace tubes) may be near thefurnace to pre-heat the temperature of the oil prior to entry into thefurnace (i.e., late-train). A typical tube-in-shell heat exchangerincludes a plurality of tubes through which the oil may flow through andaround. A hot fluid and a cold fluid enter separate chambers or tubes ofthe heat exchanger unit. The hot fluid transfers its heat to the coldfluid. The heat exchanger is designed to efficiently transfer heat fromone fluid to another. The hot and cold fluids are never combined. Heattransfer occurs through the tube wall that separates the hot and coldliquids. By employing the correct flow rate and maximizing the area ofthe partition, heat exchanger performance can be optimally controlled. Avariety of other heat exchanger designs, such as spiral heat exchangers,tube-in-tube heat exchangers and plate-and-frame heat exchangers operateessentially on the same principles.

During normal use with contact between the oil and the heat exchanger,corrosion and the build-up of deposits occurs. This build-up of depositsis often called fouling. Fouling adversely impacts the optimal controlof the heat exchanger. Fouling in this context is the unwanteddeposition of solids on the surfaces of the tubes of the heat exchanger,which leads to a loss in efficiency of the heat exchanger. The loss inheat transfer efficiency results in higher fuel consumption at thefurnace and reduced throughput. The buildup of foulants in fluidtransfer components results in reduced throughput, higher loads onpumping devices and plugging of downstream equipment as large pieces offoulant periodically dislodge and flow downstream. As a result, thetubes of the exchanger must be periodically removed from service to becleaned. This decreases overall facility reliability due to shutdownsfor maintenance. This also leads to increased manpower requirements dueto the number of cleaning crews required to service fouled heatexchanger and process fluid transfer tubes. Another detriment is anincrease in volatile organic emission resulting from the cleaningprocess.

During normal use, the surfaces of the tubes of the heat exchanger aresubject to corrosion as a result of the prolonged exposure to the streamof crude and other petroleum fractions. Corrosion on the surfaces of thetubes creates an uneven surface that can enhance fouling because thevarious particles found in the petroleum stream may attach themselves tothe roughened surface. Fouling is not limited solely to the crude oilsbeing processed. The vacuum residual streams are often used to heat thecrude within the tubes. These streams often contain solids and are highfouling. Fouling can be associated with other process streams includingbut not limited to process gases (e.g., air and steam).

While the problems of fouling extend beyond petroleum refining andpetrochemical processing, the presence of crude oil presents numerousobstacles in preventing fouling that are unique to petroleum refiningand petrochemical processing not present in other industries. Crude oil,in the context of fouling, is in reality more than simply a petroleumproduct produced from an underground reservoir. Crude oil is a complexmixture of organic and inorganic components which may result in avariety of foulant deposits on the surfaces of the heat exchangerincluding but not limited to both surfaces of the heat exchanger tubes,the baffles and the tube sheets. For example, crude oil as it isreceived at the refinery often contains corrosion byproducts such asiron sulfide, which are formed by the corrosion of drilling tubulars,pipelines, tanker holds and crude storage tanks. This material, underthe right conditions, will deposit within heat exchangers resulting indepositional fouling. Crude oils often contain aqueous contaminants,some of which arrive at the refinery. Desalting is used to remove mostof this material, but some of these contaminants pass through thedesalter into the crude preheat train. These dissolved salts can alsocontribute to depositional fouling. Sodium chloride and variouscarbonate salts are typical of this type of foulant deposit. As more andmore chemicals are used to enhance production of crude from oldreservoirs, additional inorganic materials are coming to the refineriesin the crude oil and potentially contributing to fouling.

Crude oils are typically blended at the refinery, and the mixing ofcertain types of crudes can lead to another type of foulant material.The asphaltenic material that is precipitated by blending ofincompatible crudes will often lead to a predominantly organic type offouling, which with prolonged heating, will form a carbonaceous orcoke-like foulant deposit. Crude oils often also contain acidiccomponents that directly corrode the heat exchanger materials as well.Naphthenic acids will remove metal from the surface and sulfidiccomponents will cause sulfidic corrosion which forms iron sulfide. Thissulfidic scale that is formed is often referred to as sulfide inducedfouling.

Synthetic crudes are derived from processing of bitumens, shale, tarsands or extra heavy oils and are also processed in refinery operations.These synthetic crudes present additional fouling problems, as thesematerials are too heavy and contaminant laden for the typical refineryto process. The materials are often pre-treated at the production siteand then shipped to refineries as synthetic crudes. These crudes maycontain fine particulate silicaceous inorganic matter, such as in thecase of tar sands. Some may also contain reactive olefinic materialsthat are prone to forming polymeric foulant deposits within heatexchangers. As can be understood from this discussion, crude oils arecomplex mixtures capable of forming a wide-range of foulant deposittypes.

There is a need to significantly reduce fouling in heat transfercomponents in refinery and petrochemical processing of crude oil, twoimportant fouling mechanisms are the chemical reaction and thedeposition of insoluble materials. In both fouling mechanisms thereduction of the viscous sub-layer (or boundary layer) close to the wallcan mitigate the fouling rate. In the case of chemical reaction, thehigh temperature at the surface of the heat transfer wall activatesmolecules to form precursors for the fouling residue. If theseprecursors are not swept out of the relatively stagnant wall region theywill associate together and deposit on the wall. A reduction of theboundary layer reduces the thickness of the stagnant region and hencethe amount of precursors available to form a fouling residue. In thecase of the deposition of insoluble materials, a reduction in theboundary layer increases the shear near the wall and hence exerts agreater force on the insoluble particle near the wall to overcome theparticle's attractive forces to the wall and hence reducing itsprobability of deposition and incorporation into the fouling residue.

When the walls of a heat exchanger become coated with deposits, a numberof difficulties ensue: (i) the heat transfer rate between the tube walland the material in the tube diminishes; (ii) temperature regulationdeteriorates, (iii) overheating often develops in the tubing, leading toshortened equipment life; (iv) shut-downs and cleaning cycles arenecessary, and the longer the exchanger tubing, the more expensive anddifficult is the cleaning job; (v) damage to the exchanger or ancillaryequipment results when reactor tubes become plugged and relief valvesburst. Fouling costs petroleum refineries significant amounts of moneyeach year due to lost efficiencies, lost throughput, and waste ofenergy. In addition, on many occasions, the refinery is forced to shutdown units. This adds significantly to the maintenance cost of theequipment and often requires replacement of the major components. Thisdowntime and the costs of unexpected/unplanned shutdowns also add to thecosts associated with fouling.

Currently, there are various techniques available for reducing foulingin refinery operations. One technique is avoiding the purchase ofhigh-fouling crudes or corrosive crudes. This, however, reduces the poolof feedstock that is potentially available to the refinery.Additionally, the crude oil can be tested to determine whether or notthe crude oil is compatible with the refinery. Again, this can reducethe feedstock potentially available to the refinery. Anti-foulant agentsmay also be added to the refinery stream. While these techniques areuseful in reducing the rate of fouling within the heat transfercomponents, fouling may still occur under certain circumstances. Theheat exchangers must still be routinely removed from service forcleaning to remove the build-up of contaminants. Furnace tubes must betaken off-line and steam-air decoked or pigged because of foulantdeposition. Other alternative cleaning methods include the use ofmechanical devices (e.g., “SPIRELF” and “brush and basket” devices).These devices, however, have low reliability and high maintenance needs.

There is a need to significantly reduce fouling in heat transfercomponents in refinery and petrochemical processing operations that doesnot encounter the drawbacks associated with the current techniques.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a heat transfercomponent that is resistant to fouling. The heat transfer component isused to either raise or lower the temperature of a process fluid orstream. The process fluid or stream is preferably crude oil based and isprocessed in a refinery or petrochemical facility. The presentinvention, however, is not intended to be limited solely to the use ofcrude oils, other process streams are considered to be well within thescope of the present invention. The heat transfer component may be aheat exchanger, a furnace, furnace tubes or any other component within arefinery or petrochemical facility that is capable of transferring heatfrom one medium to another which is also susceptible to foulingincluding but not limited to Crude Preheat, Coker preheat, FCC slurrybottoms, debutanizer exchanger/tower, other feed/effluent exchangers andfurnace air preheaters in refinery facilities and flare compressorcomponents and steam cracker/reformer tubes in petrochemical facilities.The heat transfer component contains at least one heat transfer element.It is contemplated that the heat transfer component is a heat exchangerfor heating crude oil in a refinery stream prior to the crude entering afurnace, whereby the heat exchanger is resistant to fouling. Thedescription of the present invention in the context of a heat exchangeris intended to be illustrative and not limiting the application of thepresent invention to heat exchangers. The heat exchanger may be atube-in-shell type heat exchanger having a tube bundle located within ahousing. The present invention is not intended to be limited totube-in-shell exchangers; rather, the present invention has applicationwithin other exchangers which are prone to fouling when subject topetroleum and/or vacuum residual streams. The tube-in-shell exchangerincludes a housing having a wall forming a hollow interior. The wall hasan inner surface that is adjacent the hollow interior. The heat transferelement may be a tube bundle located within hollow interior of thehousing. The crude oil is heated within the hollow interior of the heatexchanger housing as the crude oil flows over the tube bundle. The tubebundle preferably includes a plurality of heat exchanger tubes.

In accordance with the present invention, each heat exchanger tube maybe formed from an aluminum or aluminum alloy coated carbon steel or asteel composition that is resistant to sulfidation or sulfidic corrosionand fouling. The use of aluminum or aluminum alloy coated carbon steelor a steel composition that is resistant to sulfidation and foulingsignificantly reduces fouling and corrosion, which produces numerousbenefits including an increase in heating efficiency, a reduction in theoverall amount of energy needed to heat the crude oil, an increase inrefinery throughput and a significant reduction in refinery downtime.

It is preferable that at least one of the interior surface of the wallof the heat transfer component and the inner and/or outer surfaces ofthe plurality of heat exchanger tubes having a surface roughness of lessthan 40 micro inches (1.1 μm). Preferably, the surface roughness is lessthan 20 micro inches (0.5 μm). More preferably, the surface roughness isless than 10 micro inches (0.25 μm). It is contemplated that both theinner and outer surfaces of the plurality of heat exchanger tubes mayhave the above-mentioned surface roughness. Such a surface roughnesssignificantly reduces fouling. The smooth surface within the innerdiameter of the tubes reduces fouling of the petroleum stream flowingthrough the tubes. The smooth surfaces on the outer diameter of thetubes and on the inner surface of the housing will reduce fouling of thevacuum residual stream within the housing. It is also contemplated thatthe surfaces of the baffles located within the heat exchanger and thesurfaces of the tube sheets, which secure the tubes in place may alsohave the above-mentioned surface roughness. Such a surface roughnesswould significantly reduce fouling on these components.

In accordance with another aspect of the present invention, theplurality of heat exchanger tubes are preferably formed from a steelcomposition with a chromium enriched layer. The composition of the steelforming the heat exchanger tubes is preferably formed from a metalcomposition containing X, Y and Z. In the context of the presentinvention, X denotes a metal that is selected from the group consistingof Fe, Ni, and Co. The group also contains mixtures of these components.Y denotes Cr. Finally, Z denotes at least one alloying element selectedfrom the group consisting of Si, Al, Mn, Ti, Zr, Hf, V, Nb, Ta, Mo, W,Sc, Y, La, Ce, Pt, Cu, Ag, Au, Ru, Rh, Ir, Ga, In, Ge, Sn, Pb, B, C, N,O, P, and S. While other compositions are considered to be within thescope of the present invention, the above-described composition has beenfound to reduce fouling. The use of an aluminum or aluminum alloy coatedcarbon steel has also been found to reduce fouling and is considered tobe within the scope of the present invention.

Each of the plurality of heat exchanger tubes has a Cr-enriched layer.The Cr-enriched layer is formed on the tube and is formed from a steelhaving a similar composition to the above-described steel composition X,Y and Z. The Cr-enriched layer differs from the remaining portion of theheat exchanger tube in that the ratio of Y to X in the Cr-enriched layerbeing greater than the ratio of Y to X in the remaining portion of thetube. The Cr-enriched layer has a surface roughness of less than 40micro inches (1.1 μm), preferably less than 20 micro inches (0.5 μm) andmore preferably less than 10 micro inches (0.25 μm). The enriched layeris preferably formed on both the inner diameter surface and the outerdiameter surface of the tube. The surfaces of the baffles and the tubesheets may also include a Cr-enriched and reduced surface roughnesslayer.

In accordance with another aspect of the present invention, it iscontemplated that the Cr-enriched layer may be formed using one ofseveral techniques. The Cr-enriched layer may be formed byelectro-polishing the tube in a suitable solution (which may containchromic acid when 5-chrome steels are used). Electro-polishing iseffective when the Cr content in the steel composition is less thanabout 15 wt. %. While the concept of electro-polishing is known, the useof electro-polishing has primarily been limited to stainless steelswherein the Cr content in the steel composition is greater than about 18wt. % and not for low-chromium steels such as a 5-chrome steel or acarbon steel.

The formation of the Cr-enriched layer is not limited to the use ofelectro-polishing; rather, numerous other formation techniques areconsidered to be well within the scope of the present inventionincluding but not limited to electroplating, bright annealing,passivation, thermal spray coating, laser deposition, sputtering,physical vapor deposition, chemical vapor deposition, plasma powderwelding overlay, cladding, and diffusion bonding. It is contemplatedthat the corrosion resistant material, disclosed herein, may be used inother applications to reduce corrosion and fouling.

Each of the surfaces in the heat transfer components and particularlythe heat exchanger tubes in accordance with the present inventionpreferably has a protective layer formed thereon. The surfaces of thebaffles and the tube sheets may also include an enriched layer. Theprotective layer is preferably formed on the outer surface of theCr-enriched layer. The protective layer may be an oxide layer, a sulfidelayer, an oxysulfide layer or any combination thereof. The protectivelayer preferably includes a material selected from the group consistingof a magnetite, an iron-chromium spinel, a chromium oxide, oxides of thesame and mixtures thereof. It is contemplated that the protective layermay contain a mixed oxide sulfide thiospinel. In the accordance with thepresent invention, the protective layer is preferably formed on theCr-enriched layer after the heat exchanger tubes are located within theexchanger and the heat exchanger is operational. The protective layerforms when the Cr-enriched layer is exposed to the process streams(e.g., petroleum stream or vacuum residual stream or air) and hightemperatures. The temperature at which the protective layer formsvaries. In a late-train heat exchanger applications, the protectivelayer forms at temperatures up to 400° C. In applications in a furnaceor outside the late-train heat exchanger, the protective layer forms attemperatures up to 600° C. In petrochemical applications including usein steam cracker and reformer tubes, the protective layer forms attemperatures up to 1100° C. The temperatures utilized during theformation of the protective layer will be dependent on the metallurgy ofthe steel being acted upon. The skilled artisan can easily determine theupper temperature constraints based on the steel's metallurgy.

It has also been found that aluminum or aluminum alloy coated carbonsteels are effective in reducing fouling. The surfaces of these coatedsteels have a surface roughness of less than 40 micro inches (1.1 μm),preferably less than 20 micro inches (0.5 μm) and more preferably lessthan 10 micro inches (0.25 μm). Similarly, titanium and titanium alloyscan be effective in reducing fouling. The desired surface roughness maybe obtained by electropolishing or honing the aluminum or titaniumcoating. The desired surface roughness may also be obtained by abrasivefinishing methods including but not limited to precision grinding,microgrinding, mechanical polishing, lapping and heat treatment duringthe coated strip forming process.

It is another aspect of the present invention to provide a method ofreducing fouling in a refinery or petrochemical facility. The method mayresult in significant cost savings because the number of scheduleddowntimes to address heat transfer component fouling is significantlyreduced. Furthermore, the heat transfer components operate moreefficiently because the harmful effects of fouling are reduced. Thepresent method is especially well suited for existing heat exchangers,which may presently be plagued with fouling. The method of reducingfouling in accordance with the present invention includes removing theexisting heat exchanger tubes from the heat exchanger. The methodfurther includes installing a plurality of replacement heat exchangertubes. Each of the replacement heat exchanger tubes being formed from asteel composition that is resistant to sulfidation or sulfidic corrosionand corrosion induced fouling. It is preferable that each of thereplacement heat exchanger tubes has a surface roughness of less than 40micro inches (1.1 μm). The surface roughness is preferably less than 20micro inches (0.5 μm) and more preferably less than 10 micro inches(0.25 μm).

While it is preferable to replace all of the existing heat exchangertubes with replacement tubes having the above-described construction inorder to maximize the reduction in fouling, the present invention is notintended to be so limited. It is also contemplated that only a portionof the existing heat exchanger tubes be replaced with replacement tubes.While such a construction may not result in the same reduction infouling, a degree of fouling mitigation will be obtained. Thedetermination of the number and location of existing tubes to bereplaced by the replacement tubes can be determined by a physicalinspection of the tubes within the bundle within the heat exchanger. Itis contemplated that the existing tubes containing little or no foulingmay remain. The present invention is not limited to retrofittingexisting heat transfer components; rather, it is contemplated that theheat transfer components which exhibit fouling may be replaced with anew heat transfer component having the same desired materialcompositions and surface roughness described herein. Furthermore, it iscontemplated that fouling can be mitigated in new refinery and/orpetrochemical processing lines by installing heat transfer componentshaving the same desired material compositions and surface roughnessdescribed herein.

It is another aspect of the present invention to reduce sulfidation orsulfidic corrosion and corrosion induced fouling. While the primaryobjective of the present invention is to provide such resistance tocorrosion and fouling in the context of heat transfer components subjectto a flow of crude oil, the present invention is not intended to be solimited. It is contemplated that the present invention is suitable foruse in other refining applications where the mitigation of fouling is aconcern. In accordance with this aspect of the present invention, amethod of providing sulfidation or sulfidic corrosion resistance andcorrosion induced fouling resistance is disclosed. The method issuitable for use on a metal surface that is subject to a process stream(e.g., stream of crude oil or distilled fractions of crude oil) at hightemperatures. In a late-train heat exchanger applications, theprotective layer forms at temperatures up to 400° C. In applications ina furnace or outside the late-train heat exchanger, the protective layerforms at temperatures up to 600° C. In petrochemical applicationsincluding use in steam cracker and reformer tubes, the protective layerforms at temperatures up to 1100° C.

It is another aspect of the present invention to combine corrosionresistance with a desired surface smoothness, which has synergisticimpact on fouling mitigation. A smooth surface alone will reduce foulingtemporarily, but with time and corrosion, the smoothness is lost and sois the initial benefit. Similarly, a rough textured, thoughcorrosion-resistant surface is equally less effective at foulantreduction. In contrast, a smooth, corrosion-resistant surface willprovide a long-lasting foulant resistant surface.

It is another aspect of the present invention to provide a corrosionresistant barrier layer for use in a refinery and/or petrochemicaloperation. The corrosion resistant barrier layer may include a steelcomposition layer comprising X, Y, and Z. A Cr-enriched layer is formedon the steel composition layer, wherein the Cr-enriched layer also beingformed from X, Y and Z, wherein the ratio of Y to X in the Cr-enrichedlayer being greater than the ratio of Y to X in the steel compositionlayer. The Cr-enriched layer has a surface roughness of less than 40micro inches (1.1 μm). Preferably, the surface roughness is less than 20micro inches (0.5 μm). Even more preferable is a surface roughness ofless than 10 micro inches (0.25 μm). The corrosion resistant layerfurther includes an protective layer formed on the Cr-enriched layer.

It is an aspect of the present invention to provide a heat transfercomponent for heating a process stream. The heat transfer componentincludes a housing, at least one heat transfer element located withinthe housing for heating the process stream, and one of a vibrationproducing device to impart a vibrational force to the tube bundle and apulsation producing device for apply pressure pulsations to the crudeoil flowing through the heat exchanger. At least one of the innersurface of the housing and the at least one heat transfer element havinga surface roughness of less than 40 micro inches (1.1 μm). The surfaceroughness is preferably less than 20 micro inches (0.5 μm) and morepreferably less than 10 micro inches (0.25 μm).

It is another aspect of the present invention to provide a method ofreducing fouling in a heat transfer component for a process stream. Theheat transfer component having at least one heat transfer element havinga surface roughness of less than 40 micro inches. The method includesapplying one of fluid pressure pulsations to the process stream flowingthrough the at least one heat transfer element and vibration to the heattransfer component to effect a reduction of the viscous boundary layeradjacent the at least one heat transfer element to reduce the incidenceof fouling and promote heat transfer from the heat transfer element tothe process stream.

Another aspect of the present invention is to provide a method ofproviding sulfidation corrosion resistance and corrosion induced foulingresistance to a metal surface that is subject to a process stream athigh temperatures. The method includes providing a metal layer formedfrom a steel composition comprising X, Y, and Z, wherein X is a metalselected from the group consisting of Fe, Ni, Co and mixtures thereof,wherein is Y is Cr, and wherein Z is at least one alloying elementselected from the group consisting of Si, Al, Mn, Ti, Zr, Hf, V, Nb, Ta,Mo, W, Sc, Y, La, Ce, Pt, Cu, Ag, Au, Ru, Rh, Ir, Ga, In, Ge, Sn, Pb, B,C, N, O, P, and S, wherein a Cr-enriched layer is located on the metallayer, wherein the Cr-enriched layer also being formed from the steelcomposition X, Y, and Z, wherein the ratio of Y to X in the Cr-enrichedlayer being greater than the ratio of Y to X in the metal layer. Themethod also includes forming an protective layer on a surface of theCr-enriched layer; and applying one of fluid pressure pulsations to theprocess stream flowing past the metal surface and vibration to the metallayer to effect a reduction of the viscous boundary layer adjacent themetal layer to reduce the incidence of fouling and promote heat transferfrom the metal surface to the process stream.

It is another aspect of the present invention to provide a corrosionresistant barrier layer on a heat exchanger component with theapplication of vibration, pulsation or other internal turbulencepromoters.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in connection with the followingdrawings in which like reference numerals designate like elements andwherein:

FIG. 1 is an example of heat exchanger having a plurality of heatexchanger tubes for use in a refinery operation;

FIG. 2 is a schematic view illustrating the various layers forming thesteel composition utilized in forming the heat transfer components inaccordance with an embodiment of the present invention;

FIG. 3 is a schematic view illustrating the various layers forming thealuminum clad carbon steel utilized in forming the heat transfercomponents in accordance with an another embodiment of the presentinvention;

FIG. 4 is a partial sectional view of a heat exchanger tube inaccordance with the present invention;

FIGS. 5 and 6 are images illustrating the fouling on a conventional heatexchanger tube after a field trial; and

FIGS. 7 and 8 are images illustrating the significant reduction infouling on a heat exchanger tube in accordance with the presentinvention after a field trial.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will now be described in greater detail inconnection with the attached figures. FIG. 1 is a tube-in-shell heatexchanger 10, which is located upstream from a furnace (not shown) andemploys the principles of the present invention. The tube-in-shell heatexchanger 10 disclosed herein illustrates one application of the presentinvention to reduce sulfidation or sulfidic corrosion and depositionalfouling in refinery and petrochemical applications. The tube-in-shellexchanger 10 is just one heat transfer component falling under the scopeof the corrosion reduction and fouling mitigation measures in accordancewith the present invention. The principles of the present invention areintended to used in other heat exchangers including but not limited tospiral heat exchangers, tube-in-tube heat exchangers and plate-and-frameheat exchangers having at least one heat transfer element. Theprinciples of the present invention are intended to be employed in otherheat transfer components including furnaces, furnace tubes and otherheat transfer components which may be prone to petroleum and/or vacuumresidual fouling. The heat exchanger 10 is used to pre-heat crude oil ina refinery operation prior to entry into the furnace. The heat exchanger10 includes a housing or shell 11, which surrounds and forms a hollowinterior 12. A bundle 13 of heat exchanger tubes 14 is located withinthe hollow interior 12, as shown in FIG. 1. The bundle 13 includes aplurality of tubes 14. The tubes 14 may be arranged in a triangularconfiguration or a rectangular configuration. Other tube arrangementsare contemplated and considered to be well within the scope of thepresent invention. Each tube 14 has a generally hollow interior 15 suchthat the crude oil to be heated flows there through. The heating orwarming fluid (e.g., vacuum residual stream) flows through the hollowinterior 12 to pre-heat the crude oil stream as the stream flows throughthe hollow interior 15 towards the furnace. Alternatively, it iscontemplated that the crude oil may flow through the hollow interior 12of the housing 11. The housing 11 and the tubes 14 are preferably formedfrom a steel composition. It is contemplated that the housing 11 and thetubes 14 may be formed from the same material. It is also contemplatedthat the housing 11 and the tubes 14 may be formed from differentmaterials. Typically, the tubes and the housing are formed from a carbonor low chromium content steel.

As described above, heat exchangers are typically subject to foulingafter prolonged exposure to crude oil. The presence of fouling reducesthe performance of the heat exchanger. FIGS. 5 and 6 illustrate theeffects of fouling on the surface of a heat exchanger tube. The presenceof fouling reduces throughput and increases fuel consumption. FIGS. 5and 6 illustrate the amount of fouling present within the heat exchangertube after five months of operation. This fouling represents anapproximately 31% reduction in the heat exchanger efficiency in therefinery. The foulant contains sodium chloride, iron sulfide andcarbonaceous materials. As shown in FIGS. 5 and 6, significant amountsof pitting are present. Pitting can further exacerbate the foulingproblem.

By contrast, FIGS. 7 and 8 illustrate the reduction in fouling utilizingheat exchanger tubes 14 which embody the principles of the presentinvention. The surface cross-sections illustrated in FIGS. 7 and 8illustrate a marked reduction in fouling. These tubes were located inthe same heat exchanger and subject to the same operating conditionsover the same five month period. While the foulant present in theexchanger tube 14 also contained sodium chloride, iron sulfide andcarbonaceous material, the amount of foulant was significantly reduced.The thickness of the foulant was reduced to less than 10 microns. Thetubes having the reduced surface roughness also exhibited less pitting.The conventional tubes illustrated in FIGS. 5 and 6 exhibited a meanfoulant deposit weight density of 46 mg/cm². By contrast, the tubes 14constructed using principles in accordance with the present inventionillustrated at least 50% reduction in the mean foulant deposit weightdensity. The sample tubes exhibited a mean foulant deposit weightdensity of 22 mg/cm². Deposit weight density was determined by theNational Association of Corrosion Engineers (NACE) method TM0199-99. Thereduction in fouling shown in FIGS. 7 and 8 illustrate the benefits ofthe present invention.

The reduction in fouling may be obtained as a result of controlling thesurface roughness of the inner diameter surface and the outer diametersurface of the tubes 14 and/or the interior surface of the shell 11.Controlling the surface roughness of the inner diameter surface of thetubes mitigates the fouling of process fluid or crude oil within thetubes 14. Controlling the surface roughness of the outer diametersurface of the tubes 14 and the inner surface of the shell 11 mitigatesfouling associated with the heating fluid (e.g., vacuum residual)flowing within the hollow interior 12. In accordance with the presentinvention, at least one of the interior surface of the hollow interior12 and the surfaces of the tubes 14 has a surface roughness of less than40 micro inches (1.1 μm). Surface roughness can be measured in manyways. Industry prefers to use a skidded contact profilometer. Roughnessis routinely expressed as the arithmetic average roughness (Ra). Thearithmetic average height of roughness component of irregularities fromthe mean line is measured within the sample length L. The standardcut-off is 0.8 mm with a measuring length of 4.8 mm. This measurementconforms to ANSI/ASME B46.1 “Surface Texture-Surface Roughness, Wavinessand Lay,” which was employed in determining the surface roughness inaccordance with the present invention. A uniform surface roughness ofless than 40 micro inches (1.1 μm) produces a significant reduction infouling.

Further reductions in surface roughness are desirable. It is preferablethat the surface roughness be below 20 micro inches (0.5 μm). It is morepreferable that the surface roughness be below 10 micro inches (0.25μm). It is preferable that both the inner diameter surface and the outerdiameter surface have the described surface roughness. The interiorsurface of the wall may also have the desired surface roughness toreduce fouling within the housing. The desired surface roughness may beobtained through various techniques including but not limited tomechanical polishing and electro-polishing. In the samples illustratedin FIGS. 5 and 6, the surface roughness of the tubes was variablebetween 38 and 70 micro inches. The tubes in FIGS. 5 and 6 were notpolished. The tubes illustrated in FIGS. 7 and 8, which form the basisfor the present invention were polished to a more uniform 20 microinches (0.5 μm). This was accomplished using conventional mechanicalpolishing techniques. The tubes were then electro-polished in an acidicelectrolyte to produce a reflective surface having a surface roughnessbelow 10 micro inches (0.25 μm). The treated tubes exhibited a markedreduction in fouling.

In accordance with the present invention, it is preferable that thetubes 14 be formed from a composition that is resistant to sulfidationor sulfidic corrosion and depositional fouling. The use of such acomposition significantly reduces fouling, which produces numerousbenefits including an increase in heating efficiency, a reduction in theamount of energy needed to pre-heat the crude oil, and a significantreduction in refinery downtime and throughput. It is preferable that thetubes 14 and/or the housing 11 of the pre-heat exchanger have severallayers, as illustrated in FIGS. 2 and 4. The primary layer 21 is a steelcomposition containing three primary components or constituents X, Y andZ. X denotes a metal that is selected from the group preferablyconsisting of Fe, Ni, and Co. X may also contain mixtures of Fe, Ni andCo. Y denotes Cr. In accordance with the present invention, a steelcomposition contains Cr at least greater than 1 wt. % based on thecombined weight of the three primary constituents X, Y and Z. Higher Crcontents are desirable for improved sulfidation or sulfidic corrosionresistance. It is preferable that the Cr content be higher than 5 wt. %based on the combined weight of three primary constituents X, Y and Z.It is more preferable that the Cr content be higher than 10 wt. % basedon the combined weight of three primary constituents X, Y and Z. Z ispreferably an alloying element.

In accordance with the present invention, Z preferably includes at leastone alloying element selected from the group consisting of Si, Al, Mn,Ti, Zr, Hf, V, Nb, Ta, Mo, W, Sc, Y, La, Ce, Pt, Cu, Ag, Au, Ru, Rh, Ir,Ga, In, Ge, Sn, Pb, B, C, N, O, P, and S. Z may also contain mixtures ofSi, Al, Mn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Sc, Y, La, Ce, Pt, Cu, Ag, Au,Ru, Rh, Ir, Ga, In, Ge, Sn, Pb, B, C, N, O, P, and S. The weight percentof an alloying element is preferably higher than 0.01 wt. %, and morepreferably higher than 0.05 wt. %, and most preferably higher than 0.1wt. %, based on the combined weight of three primary constituents X, Yand Z. The combined weight percent of all alloying elements in a steelcomposition is preferably less than 10 wt. %, and more preferably lessthan 5 wt. %, based on the combined weight of three primary constituentsX, Y and Z. While other compositions are considered to be within thescope of the present invention, the above-described composition has beenfound to reduce fouling.

Table 1 illustrates non-limiting examples of a steel composition that isresistant to sulfidation or sulfidic corrosion and corrosion inducedfouling for use in both refining and petrochemical applications. Othermaterials exhibiting similar properties are considered to be well withinthe scope of the present invention provided such materials fall withinthe scope of the prescribed ranges. TABLE 1 Constit- uent Name UNSConstituent Y in (Grade) Number X in wt. % wt. % Constituent Z in wt. %T11 K11562 Balanced Fe 1.25Cr 0.5Mo, 0.5Si, 0.3Mn, 0.15C, 0.045P, 0.045ST22 K21590 Balanced Fe 2.25Cr 1.0Mo, 0.5Si, 0.3Mn, 0.15C, 0.035P, 0.035ST5  S50100 Balanced Fe 5Cr 0.5Mo, 0.5Si, 0.3Mn, 0.15C, 0.04P, 0.03S T9 J82090 Balanced Fe 9Cr 1.0Si, 0.35Mn, 0.02C, 0.04P, 0.045S 409 S40900Balanced Fe 10.5Cr 1.0Si, 1.0Mn, 0.5Ni, 0.5Ti, 0.08C, 0.045P, 0.045S 410S41000 Balanced Fe 11.5Cr 0.15C, 0.045P, 0.03S 430 S43000 Balanced Fe16Cr 1.0Si, 1.0Mn, 0.12C, 0.045P, 0.03S XM-27 S44627 Balanced Fe 25Cr0.5Ni, 0.75Mo, 0.4Si, 0.4Mn, 0.05Nb, 0.2Cu, 0.01C, 0.02P, 0.02S, 0.015NSeaCure S44660 Balanced Fe 25Cr 1.5Ni, 2.5Mo, 1.0Si, 1.0Mn, 0.05Nb,0.2Cu, 0.025C, 0.04P, 0.03S, 0.035N 304 S30400 Bal. Fe, 8Ni 18Cr 2.0Mn,0.75Si, 0.08C, 0.04P, 0.03S   304L S30403 Bal. Fe, 8Ni 18Cr 2.0Mn,0.75Si, 0.035C, 0.04P, 0.03S  309S S30908 Bal. Fe, 12Ni 22Cr 2.0Mn,0.75Si, 0.75Mo, 0.08C, 0.045P, 0.03S 310 S31000 Bal. Fe, 19Ni 24Cr2.0Mn, 1.5Si, 0.75Mo, 0.25C, 0.045P, 0.03S 316 S31600 Bal. Fe, 11Ni 16Cr2.0Mn, 0.75Si, 2.0Mo, 0.08C, 0.04P, 0.03S   316L S31603 Bal. Fe, 11Ni16Cr 2.0Mn, 0.75Si, 2.0Mo, 0.035C, 0.04P, 0.03S 321 S32100 Bal. Fe, 9Ni17Cr 2.0Mn, 0.75Si, 0.4Ti, 0.08C, 0.045P, 0.03S 2205  S32205 Bal.Fe:4.5Ni 22Cr 2.0Mn, 1.0Si, 3.0Mo, 0.03C, 0.14N, 0.03P, 0.02S 2507 S32507 Bal. Fe:6Ni 24Cr 1.2Mn, 0.8Si, 3.0Mo, 0.5Cu, 0.03C, 0.2N, 0.035P,0.02S AL-6XN N08367 Bal. Fe:24Ni 20Cr 6.2Mo, 0.4Si, 0.4Mn, 0.22N, 0.2Cu,0.02C, 0.02P, 0.03S, 0.035N Alloy N08800 Bal. Fe:30Ni 19Cr 0.15Ti,0.15Al 800

The chromium enrichment at the surface of the non-fouling surface isadvantageous. Therefore, the steel composition preferably includes achromium enriched layer 22. The Cr-enriched layer 22 is formed on theprimary layer 21. The layer 22 may be formed on both the inner surfaceand the exterior surface of the tubes. The thickness of the Cr-enrichedlayer 22 is greater than 10 angstroms. The Cr-enriched layer 22 containsthe same three primary components or constituents X, Y and Z. X denotesa metal that is selected from the group preferably consisting of Fe, Ni,and Co. X may also contain mixtures of Fe, Ni, Co and Ti. Y denotes Cr.It is contemplated that Y may also comprise Ni, O, Al, Si and mixturesthereof. The percentage of Cr is higher in layer 22 when compared to theprimary layer 21. In accordance with the present invention, Cr contentin layer 22 is at least greater than 2 wt. % based on the combinedweight of three primary constituents X, Y and Z. It is preferable thatthe Cr content be higher than 10 wt. % based on the combined weight ofthree primary constituents X, Y and Z. It is more preferable that the Crcontent be higher than 30 wt. % based on the combined weight of threeprimary constituents X, Y and Z. In the layer 22, the ratio of Y to X isgreater than the ratio of Y to X in the layer 21. The ratio should begreater by a factor of at least 2. The ratio should preferably begreater by a factor of at least four. More preferably, the ratio shouldbe a greater by a factor of eight. Z is preferably an alloying element.

For example, 5-chrome steel (T5) nominally contains about 5 wt. %chromium per about 95 wt. % iron to give an untreated surface ratio of0.05 in the primary layer 21. In the Cr-enriched layer 22, the ratioincreased to at least 0.1, preferably to 0.2 and most preferably to 0.4chromium atoms per iron atom in the surface layer of the heat exchangertube. For 316L stainless steel, which has nominally 16 wt. % Cr, 11 wt.% Ni, 2 wt. % Mn, 2 wt. % Mo, the bulk ratio of chromium to iron wouldbe 16/69=0.23. After treatment to enrich the surface chromium, the ratiomay rise to at least 0.46, preferably 0.92 and most preferably 1.84.

In the Cr-enriched layer 22, Z preferably includes at least one alloyingelement selected from the group consisting of Si, Al, Mn, Ti, Zr, Hf, V,Nb, Ta, Mo, W, Sc, Y, La, Ce, Pt, Cu, Ag, Au, Ru, Rh, Ir, Ga, In, Ge,Sn, Pb, B, C, N, O, P, and S. The weight percent of an alloying elementis preferably higher than 0.01 wt. %, and more preferably higher than0.05 wt. %, and most preferably higher than 0.1 wt. %, based on thecombined weight of three primary constituents X, Y and Z.

It is contemplated that the Cr-enriched layer 22 may be formed on twosides of the primary layer 21 such that both the interior surface andthe exterior surface contain a Cr-enriched layer. The Cr-enriched layer22 may be formed on the primary layer 21 using one of severaltechniques. The Cr-enriched layer may be formed by electro-polishing thetube in a solution containing chromic acid. This is effective when theCr content in the steel composition is less than about 15 wt. %. It isalso contemplated that the Cr-enriched layer 22 may be formed usingvarious other formation techniques including but not limited toelectroplating chromium onto another alloy such as a carbon steel,bright annealing, passivation, thermal spray coating, laser deposition,sputtering, physical vapor deposition, chemical vapor deposition, plasmapowder welding overlay, cladding, and diffusion bonding. It is alsopossible to choose a high chromium alloy including but not limited to304L stainless steel, 316 stainless steel and AL6XN alloy. In accordancewith the present invention, the secondary layer 22 may be mechanicallypolished and/or electro-polished as described above in order to obtain auniform surface roughness of less than 40 micro inches (1.1 μm),preferably less than 20 micro inches (0.5 μm) and more preferably lessthan 10 micro inches (0.25 μm). The desired surface roughness can alsobe achieved using fine abrasive polishing or metal peening.

The Cr-enriched layer 22 may be formed on the primary layer 21 by brightannealing the tube. Bright annealing is an annealing process that iscarried out in a controlled atmosphere furnace or vacuum in order thatoxidation is reduced to a minimum and the surface remains relativelybright. The process conditions such as atmosphere, temperature, time andheating/cooling rate utilized during the bright annealing process willbe dependent on the metallurgy of the alloy being acted upon. Theskilled artisan can easily determine the conditions based on the alloy'smetallurgy. As a non-limiting example, the austenitic stainless steelsuch as 304L can be bright annealed in either pure hydrogen ordissociated ammonia, provided that the dew point of the atmosphere isless than −50° C. and the tubes, upon entering the furnace, are dry andscrupulously clean. Bright annealing temperatures usually are above1040° C. Time at temperature is often kept short to hold surface scalingto a minimum or to control grain growth.

In accordance with the present invention, a protective layer 23 ispreferably formed on the Cr-enriched layer 22. The Cr-enriched layer 22is necessary for the formation of the protective layer 23. Theprotective layer may be an oxide layer, a sulfide layer, an oxysulfidelayer or any combination thereof. The protective layer 23 preferablyincludes a material such as a magnetite, an iron-chromium spinel, achromium oxide, oxides of the same and mixtures thereof. The layer 23may also contain a mixed oxide sulfide thiospinel. While it is possibleto form the protective layer 23 on the Cr-enriched layer 22 prior toinstallation of the tubes 14 within the housing 11 of the pre-heatexchanger 10, the protective layer 23 is preferably formed on theCr-enriched layer 22 after the tubes 14 are located within the exchanger10 and the pre-heat exchanger is operational. The protective layer 23forms when the Cr-enriched layer is exposed to the process stream athigh temperatures. In a late-train heat exchanger application, theprotective layer forms at temperatures up to 400° C. In applications ina furnace or outside the late-train heat exchanger, the protective layerforms at temperatures up to 600° C. In petrochemical applicationsincluding use in steam cracker and reformer tubes, the protective layerforms at temperatures up to 1100° C. The thickness of the protectivelayer 23 is preferably greater than 100 nm, more preferably greater than500 nm, and most preferably greater than 1 micron. As illustrated inFIGS. 6 and 7, a field trial of 5-chrome steel revealed about 1 micronthick Cr-enriched magnetite layer formed during about 4 months ofperiod. Since the stream oil flowing within a heat exchanger tube is ahighly reducing and sulfidizing environment, the protective layer 23 canfurther convert to a mixed oxide-sulfide layer or a thiospinel-typesulfide layer after prolonged exposure. Applicants note that theformation of the protective layer 23 is a result of theelectro-polishing of the Cr-enriched layer 21.

The formation of the protective layer further reduces fouling. Thefoulants, which form on the protective layer 23 exhibit significantlyless adhesion characteristics when compared to foulants, which form onsurfaces that do not have the protective layer. One benefit of thisreduced adhesion lies in the cleaning of the heat exchange surface. Lesstime is required to remove any foulants from the tubes. This results ina decrease in downtime such that the pre-heat exchanger can be servicedin a more efficient manner and placed back online sooner. Also, with aless adherent deposit, on-line cleaning methods may become moreeffective or at least more rapid, which will further reduce downtime andthroughput loss.

There are numerous additional benefits of reducing the surface roughnessof the tubes 14. One of the benefits is the shifting from a lineargrowth rate of the foulant, which results in the continuous thickeningof the foulant deposit; to an asymptotic growth rate which reaches afinite thickness and then stops thickening.

The tubes 14 disclosed above may be used to form new heat exchangers.The tubes 14 can also be used in existing exchangers as replacementtubes. The use of the tubes 14 should produce significant benefits inthe refinery operations. In addition to reducing fouling, there is areduction in the number of scheduled downtimes the heat exchangersoperate more efficiently because the harmful effects of fouling arereduced. In addition, as demonstrated in the field test, the use of thetubes 14 will also prolong tube life due to reduced pitting corrosion.

The tubes 14 in accordance with the present invention may be used toretrofit an existing heat exchanger during a scheduled downtime. Theexisting tubes can be removed from the heat exchanger. The tubes 14having the above described surface roughness and/or material compositionare installed in the interior 12 of the housing 11. While it ispreferable to replace all of the existing heat exchanger tubes withreplacement tubes having the above-described construction in order tomaximize the reduction in fouling, the present invention is not intendedto be so limited. It is contemplated that only a portion of the existingheat exchanger tubes be replaced with replacement tubes. While such aconstruction may not result in the same reduction in fouling, a degreeof fouling mitigation will be obtained. The determination of the numberand location of existing tubes to be replaced by the replacement tubescan be determined by a physical inspection of the tubes within thebundle within the heat exchanger. The tubes located closest to thefurnace may be more prone to fouling. As such, it is also contemplatedthat tubes located most closely to the furnace may be replaced withtubes 14.

A variation of the present invention will now be described in greaterdetail in connection with FIG. 3. FIG. 3 illustrates an aluminum oraluminum alloy coated carbon steel that may be effective in reducingcorrosion and mitigating fouling. A carbon steel layer 31 is coated orclad with an aluminum layer 32. The aluminum layer or aluminum alloy maybe applied by immersion of the steel in molten aluminum or aluminumalloy or by thermal spraying of aluminum powder or wire that isatomized. When used in a tube 14, the aluminum layer 32 is located onboth the inner diameter surface and the outer diameter surface of thetube 14 similar to the Cr-enriched layer 22.

It is another aspect of the present invention to reduce sulfidationcorrosion and depositional fouling. While the primary objective of thepresent invention is to provide such resistance to corrosion and foulingin the context of heat exchangers subject to a flow of crude oil, thepresent invention is not intended to be so limited. It is contemplatedthat the present invention is suitable for use in other refiningapplications where the mitigation of fouling is a concern. In accordancewith this aspect of the present invention, a method of providingsulfidation corrosion resistance and corrosion induced foulingresistance is disclosed. The method is suitable for use on a metalsurface that is subject to a process stream at temperatures up to 1100°C. The method includes providing a metal layer formed from a steelcomposition comprising X, Y, and Z described above. The metal layer 21preferably includes a Cr-enriched layer 22 located thereon. TheCr-enriched layer 22 may be formed from the same material X, Y and Z,however, the ratio of Y to X in the Cr-enriched layer is greater thanthe ratio of Y to X in the metal layer. A protective layer 23 is formedon the surface of the Cr-enriched layer 22. The protective layer 23 ispreferably formed by exposing the Cr-enriched layer to a crude oil orpetroleum stream at high temperatures up to 1100° C.

It is another aspect of the present invention to combine heat transfercomponents having the above described corrosion and fouling resistantmaterials with either a pulsation generating device or a vibrationalgenerating device to further reduce and mitigate fouling. The devicesare generically designated in FIG. 1 with reference numeral 3. Thedevices 3 may or may not be located on the housing.

It is contemplated that the pulsation device will comprise any means forapplying liquid pressure pulsations to the tube side liquid. In thesimplest concept, the device may comprise a reciprocating pump typemechanism with a cylinder connected to the inlet/outlet conduits of theheat transfer components and a reciprocating piston in the cylinder tovary the internal volume of the cylinder. As the piston moves within thecylinder, the liquid will alternately be drawn into the cylinder andthen expelled from it, creating pulsations in the conduit to which thedevice is connected. The use of a double-acting pump of this kind withone side connected to the inlet conduit and the other connected to theoutlet conduit is particularly desirable since it will create thedesired pressure pulsations in the heat transfer component regardless ofthe pressure drop occurring in the heat transfer component. Variation inthe frequency of the pulsations may be afforded by variations in thereciprocation speed of the piston and any desired variations inpulsation amplitude may be provided by the use of a variabledisplacement pump, e.g. a variable displacement piston pump, swashplate(stationary plate) pump and its variations such as the wobble plate(rotary plate) pump or bent axis pump.

The present invention is not intended to be limited to theabove-described pump; rather, it is contemplated that other types ofpumps may also be used as the pulsation device including diaphragm pumpsand these may be practically attractive since they offer the potentialfor activation of the diaphragm by electrical, pneumatic or directmechanical means with the movement of the diaphragm controlled toprovide the desired frequency and amplitude (by control of the extent ofdiaphragm movement). Other types may also be used but gear pumps andrelated types such as the helical rotor and multi screw pumps which givea relatively smooth (non pulsating) fluid flow are less preferred inview of the objective of introducing pulsations which disrupt theformation of the troublesome boundary layer. Other types which doproduce flow pulsations such as the lobe pump, the vane pump and thesimilar radial piston pump, are normally less preferred although theymay be able to produce sufficient pulsation for the desired purpose.Given the objective is to induce pulsations, other types of pulsator maybe used, for example, a flow interrupter which periodically interruptsthe liquid flow on the tube side. Pulsators of this type may include,for example, siren type, rotary vane pulsators in which the flowinterruption is caused by the repeated opening and closing of liquidflow passages in a stator/rotor pair, each of which has radial flowopenings which coincide with rotation of the moving rotor member. Therotor may suitably be given impetus by the use of vanes at an angle tothe direction of liquid flow, e.g. by making radial cuts in the rotordisc and bending tabs away from the plane of the disc to form the vanes.Another type is the reed valve type with spring metal vanes which coverapertures in a disc and which are opened temporarily by the pressure ofthe fluid in the transfer component, followed by a period when the vanesnaps closed until fluid pressure once more forces the vane open.

In order to optimize the impact within the exchanger, it is preferableto locate the pulsation device close to the heat transfer component inorder to ensure that the pulsations are efficiently transferred to theliquid flow in the heat transfer components, that is, the pulsations arenot degraded by passage through intervening devices such as valves.Normally, the frequency of the liquid pulsations will be in the range of0.1 Hz to 20 kHz. The amplitude of the pulsation as measured by theincremental flow rate through the heat exchange tubes could range fromabout the order of the normal heat exchanger flow rate at the lower endof the range of pulsation frequencies to less than 10⁻⁶ of the normalheat exchanger flow rate at the higher frequencies; because of pressuredrop limitations in the heat exchanger operation and/or dissipation ofhigher frequencies in the fluid, the upper limit of the pulse amplitudewill decrease with increased frequency. Thus, for example, in the lowerhalf of this frequency range, the amplitude of the pulsations could befrom about 10⁻² to about the normal flow rate and with frequencies inthe upper half of the range, from about 10⁻⁶ to 0.1 of the normal flowrate through the exchanger.

It is contemplated that the vibration producing device may be any meansthat is capable of imparting a vibration force on the heat exchangerunit. The vibration producing device may be of the kind disclosed inco-pending U.S. patent Ser. No. 11/436,802. The vibration producingdevice may be externally connected to the heat transfer component toimpart controlled vibrational energy to the heat transfer surface of theheat transfer component. The vibration producing device can take theform of any type of mechanical device that induces tube vibration whilemaintaining structural integrity of the heat exchanger. Any devicecapable of generating sufficient dynamic force at selected frequencieswould be suitable. The vibration producing device can be single device,such as an impact hammer or electromagnetic shaker, or an array ofdevices, such as hammers, shakers or piezoelectric stacks. An array canbe spatially distributed to generate the desired dynamic signal toachieve an optimal vibrational frequency. The vibration producing devicemay be placed at various locations on or near the heat transfercomponent as long as there is a mechanical link to the component.Sufficient vibration energy can be transferred to the heat transfercomponent at different vibration modes. There are low and high frequencyvibration modes of tubes. For low frequency modes (typically below 1000Hz), axial excitation is more efficient at transmitting vibrationenergy, while at high frequency modes, transverse excitation is moreefficient. The density of the vibration modes is higher at a highfrequency range than at a low frequency range (typically below 1000 Hz),and vibration energy transfer efficiency is also higher in the highfrequency range. Further, displacement of component or tube vibration isvery small at high frequency (>1000 Hz) and insignificant for potentialdamage to the heat transfer component.

It will be apparent to those skilled in the art that variousmodifications and/or variations may be made without departing from thescope of the present invention. While the present invention has beendescribed in the context of the heat exchanger in a refinery operation.The present invention is not intended to be so limited; rather, it iscontemplated that the desired surface roughnesses and materialsdisclosed herein may be used in other portions of a refinery operationwhere fouling may be of a concern. Reducing the surface smoothness ofother corrosion resistant materials such as aluminized carbon steel,titanium, electroless nickel-coated carbon steel and other corrosionresistant surfaces are extensions of this concept as delineated below.It is contemplated that the method of reducing fouling disclosed hereincan be combined with other reduction strategies to reduce fouling. Thisincludes combining the low surface roughness and/or materialcompositions disclosed herein with vibrational, pulsation, helicalshell-side baffles and internal turbulence promoters. Thus, it isintended that the present invention covers the modifications andvariations of the method herein, provided they come within the scope ofthe appended claims and their equivalents.

1. A heat transfer component for heating a process stream, comprising: ahousing having a wall forming a hollow interior, wherein the wall havingan inner surface; at least one heat transfer element located within thehousing for heating the process stream; and one of a vibration producingdevice to impart a vibrational force to the heat transfer element and apulsation producing device for apply pressure pulsations to the processstream flowing through the heat exchanger, wherein at least one of theinner surface and the at least one heat transfer element having asurface roughness of less than 40 micro inches (1.1 μm).
 2. The heattransfer component according to claim 1, wherein the surface roughnessis less than 20 micro inches (0.5 μm).
 3. The heat transfer componentaccording to claim 2, wherein the surface roughness is less than 10micro inches (0.25 μm).
 4. The heat transfer component according toclaim 1, wherein the at least one heat transfer element being formedfrom a composition that is resistant to sulfidation corrosion andcorrosion induced fouling.
 5. The heat transfer component according toclaim 4, wherein the composition is a steel composition comprising: X,Y, and Z, wherein X is a metal selected from the group consisting of Fe,Ni, Co and mixtures thereof, wherein is Y is Cr, and wherein Z is atleast one alloying element selected from the group consisting of Si, Al,Mn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Sc, Y, La, Ce, Pt, Cu, Ag, Au, Ru, Rh,Ir, Ga, In, Ge, Sn, Pb, B, C, N, O, P, and S.
 6. The heat transfercomponent according to claim 5, wherein each heat transfer elementhaving an inner surface and an exterior surface and a Cr-enriched layerformed on at least one of the inner surface and the exterior surface,wherein the Cr-enriched layer also being formed from the steelcomposition X, Y and Z, wherein the ratio of Y to X in the Cr-enrichedlayer being greater than the ratio of Y to X in the remaining portion ofthe heat transfer element.
 7. The heat transfer component according toclaim 6, wherein the Cr-enriched layer is formed by one ofelectro-polishing, electroplating, thermal spray coating, laserdeposition, sputtering, physical vapor deposition, chemical vapordeposition, plasma powder welding overlay, cladding, and diffusionbonding.
 8. The heat transfer component according to claim 7, whereinthe surface roughness of the Cr-enriched layer is less than 40 microinches (1.1 μm).
 9. The heat transfer component according to claim 8,wherein the surface roughness of the Cr-enriched layer is less than 20micro inches (0.5 μm).
 10. The heat transfer component according toclaim 9, wherein the surface roughness of the Cr-enriched layer is lessthan 10 micro inches (0.25 μm).
 11. The heat transfer componentaccording to claim 10, wherein the heat transfer component includes avibration producing device operatively connected to the housing toimpart a vibrational force to the at least one heat transfer element.12. The heat transfer component according to claim 10, wherein the heattransfer component includes a pulsation producing device for applypressure pulsations to the process stream flowing through the at leastone heat transfer element.
 13. The heat transfer component according toclaim 6, further comprising: an protective layer formed on an outersurface of the Cr-enriched layer.
 14. The heat transfer componentaccording to claim 13, wherein the protective layer comprises an oxideselected from the group consisting of a magnetite, an iron-chromiumspinel, a chromium oxide, and mixtures thereof.
 15. The heat transfercomponent according to claim 14, wherein the protective layer beingformed within the at least one heat transfer element when subjected to aprocess stream at high temperatures up to 400° C.
 16. The heat transfercomponent according to claim 14, wherein the protective layer beingformed within the at least one heat transfer element when subjected to aprocess stream at high temperatures up to 600° C.
 17. The heat transfercomponent according to claim 14, wherein the protective layer beingformed within the at least one heat transfer element when subjected to aprocess stream at high temperatures up to 1100° C.
 18. The heat transfercomponent according to claim 13, wherein the heat transfer componentincludes a vibration producing device operatively connected to thehousing to impart a vibrational force to the at least one heat transferelement.
 19. The heat transfer component according to claim 13, whereinthe heat transfer component includes a pulsation producing device forapply pressure pulsations to the process stream flowing through the atleast one heat transfer element.
 20. The heat transfer componentaccording to claim 1, wherein the at least one heat transfer elementbeing formed from a carbon steel having an aluminum or aluminum alloylayer located thereon.
 21. The heat transfer component according toclaim 20, wherein the heat transfer component includes a vibrationproducing device operatively connected to the housing to impart avibrational force to the at least one heat transfer element.
 22. Theheat transfer component according to claim 20, wherein the heat transfercomponent includes a pulsation producing device for apply pressurepulsations to the process stream flowing through the at least one heattransfer element.
 23. The heat transfer component according to claim 20,wherein the surface roughness is less than 20 micro inches (0.5 μm). 24.The heat transfer component according to claim 23, wherein the surfaceroughness is less than 10 micro inches (0.25 μm).
 25. The heat transfercomponent according to claim 1, wherein the heat transfer componentincludes a vibration producing device operatively connected to thehousing to impart a vibrational force to the at least one heat transferelement.
 26. The heat transfer component according to claim 1, whereinthe heat transfer component includes a pulsation producing device forapply pressure pulsations to the process stream flowing through the atleast one heat transfer element.
 27. The heat transfer componentaccording to claim 1, wherein the at least one heat transfer elementbeing formed from a carbon steel having an aluminum or aluminum alloylayer located thereon.
 28. The heat transfer component according toclaim 27, wherein the surface roughness is less than 20 micro inches(0.5 μm).
 29. The heat transfer component according to claim 28, whereinthe surface roughness is less than 10 micro inches (0.25 μm).
 30. Theheat transfer component according to claim 27, wherein the heat transfercomponent includes a vibration producing device operatively connected tothe housing to impart a vibrational force to the at least one heattransfer element.
 31. The heat transfer component according to claim 27,wherein the heat transfer component includes a pulsation producingdevice for apply pressure pulsations to the process stream flowingthrough the at least one heat transfer element.
 32. A method of reducingfouling in a heat transfer component for a process stream, wherein theheat transfer component having at least one heat transfer element havinga surface roughness of less than 40 micro inches, the method comprising:applying one of fluid pressure pulsations to the process stream flowingthrough the at least one heat transfer element and vibration to the heattransfer component to effect a reduction of the viscous boundary layeradjacent the at least one heat transfer element to reduce the incidenceof fouling and promote heat transfer from the heat transfer element tothe process stream.
 33. The method of reducing fouling according toclaim 32, wherein the surface roughness of less than 20 micro inches.34. The method of reducing fouling according to claim 33, wherein thesurface roughness of less than 10 micro inches.
 35. The method ofreducing fouling according to claim 32, wherein the method comprising:applying fluid pressure pulsations to the process stream.
 36. The methodof reducing fouling according to claim 32, wherein the methodcomprising: applying vibration to the at least one heat transferelement.
 37. A method of providing sulfidation corrosion resistance andcorrosion induced fouling resistance to a metal surface that is subjectto a process stream at high temperatures, the method comprising:providing a metal layer formed from a steel composition comprising X, Y,and Z, wherein X is a metal selected from the group consisting of Fe,Ni, Co and mixtures thereof, wherein is Y is Cr, and wherein Z is atleast one alloying element selected from the group consisting of Si, Al,Mn, Ti, Zr, Hf, V, Nb, Ta, Mo, W, Sc, Y, La, Ce, Pt, Cu, Ag, Au, Ru, Rh,Ir, Ga, In, Ge, Sn, Pb, B, C, N, O, P, and S, wherein a Cr-enrichedlayer is located on the metal layer, wherein the Cr-enriched layer alsobeing formed from the steel composition X, Y, and Z, wherein the ratioof Y to X in the Cr-enriched layer being greater than the ratio of Y toX in the metal layer; forming an protective layer on a surface of theCr-enriched layer; and applying one of fluid pressure pulsations to theprocess stream flowing past the metal surface and vibration to the metallayer to effect a reduction of the viscous boundary layer adjacent themetal layer to reduce the incidence of fouling and promote heat transferfrom the metal surface to the process stream.
 38. The method accordingto claim 37, wherein the method comprising applying fluid pressurepulsations to the process stream.
 39. The method according to claim 37,wherein the method comprising applying vibration to the metal layer. 40.The method according to claim 37, wherein the Cr-enriched layer having asurface roughness of less than 40 micro inches (1.1 μm).
 41. The methodaccording to claim 40, wherein the Cr-enriched layer having a surfaceroughness of less than 20 micro inches (0.5 μm).
 42. The methodaccording to claim 41, wherein the Cr-enriched layer having a surfaceroughness of less than 10 micro inches (0.25 μm).
 43. The methodaccording to claim 37, wherein forming the protective layer comprisingexposing the Cr-enriched layer to a process stream at high temperaturesup to 400° C.
 44. The method according to claim 37, wherein forming theprotective layer comprising exposing the Cr-enriched layer to a processstream at high temperatures up to 600° C.
 45. The method according toclaim 37, wherein forming the protective layer comprising exposing theCr-enriched layer to a process stream at high temperatures up to 1100°C.
 46. The method according to claim 37, wherein the protective layercomprises an oxide selected from the group consisting of a magnetite, aniron-chromium spinel, a chromium oxide, and mixtures thereof.
 47. Themethod according to claim 46, wherein forming the protective layercomprising exposing the Cr-enriched layer to a crude stream at hightemperatures up to 400° C.
 48. The method according to claim 46, whereinforming the protective layer comprising exposing the Cr-enriched layerto a process stream at high temperatures up to 600° C.
 49. The methodaccording to claim 46, wherein forming the protective layer comprisingexposing the Cr-enriched layer to a process stream at high temperaturesup to 1100° C.